The energy-transducing nicotinamide transhydrogenases (THs) of mammalian and bacteria are structurally related membrane-bound enzymes that catalyze the direct transfer of a hydride ion between NAD(H) and NADP(H) in a reaction coupled to transmembrane proton translocation. The NADPH produced by TH is to reduce H2O2, which is capable of causing oxidative damage to intramitochondrial DNA and proteins, and initiating lipid peroxidation. Therefore, in order to understand the proton translocation mechanism and the reaction catalyzed by these enzymes a detailed knowledge of their three dimensional structure is essential. Weakly diffracting, highly anisotropic and radiation sensitve crystals of the alfa-1 subunit of R. rubrum TH have been obtained. These crystals diifract only to 4 E resolution using in-house x-ray source, whereas, the same crystals diffract to 2.7 E on BL7-1.